1. Field of the Invention
The present invention relates to a solar cell adapted for use in various electronic equipment or electric power supply devices, and more particularly to a modular solar cell with an improved protective member constituting protective means therefor.
2. Related Background Art
Because of the recent forecast for the warming of the entire earth by the greenhouse effect resulting from the increase of atmospheric CO.sub.2, the need has become stronger for clean energy production without CO.sub.2 discharge. However, nuclear power generation, which is free from CO.sub.2 discharge, is still associated with the problem of disposal of radioactive products, so that clean energy with improved safety is desired. Among the future candidates of such clean energy, the solar cell is very desirable because of its cleanness, safety, and easy handling.
Among various solar cells, those based on non-monocrystalline semiconductors such as amorphous silicon or copper indium selenide are the subjects of intensive developmental works, as these materials can be prepared in a large area and with a low production cost. If impact resistance or flexibility is required, such solar cells are often formed on a metal substrate such as of stainless steel.
For the purpose of reducing the weight of the solar cell formed on the stainless steel substrate, ensuring flexibility, and providing weather resistance and impact resistance, such solar cell is sealed with a resin such as a fluorinated resin or ethylene vinyl acetate (EVA). After such resin sealing, the end portions of the solar cell are covered with a protective frame composed of a metal such as aluminum or a polymer such as polyvinyl chloride or synthetic rubber, for the purpose of protecting the end faces and providing a support member. Particularly if flexibility is required for the solar cell module, there is usually employed a flexible polymer such as synthetic rubber of soft polyvinyl chloride.
The fixation between the end portions of the sealed solar cell and the protective frame, for example of polymer material, is achieved by an adhesive material, after the contact faces are pre-treated with plasma, strong acid, or strong alkali for facilitating the adhesion.
FIG. 1 is a schematic cross-sectional view of a conventional prior art solar cell.
In FIG. 1 there are shown a solar cell device 401 formed on a conductive substrate; a resinous covering material 404 for sealing said solar cell device 401; a resin-sealed solar cell 402; and a protective frame 403 composed of flexible resin. The outermost layer of the resin 404 is usually composed of a fluorinated resin, in consideration of weather resistance. Also the protective frame 403 is usually composed of synthetic rubber or soft polyvinyl chloride, in consideration of the weather resistance and flexibility.
Since the fluorinated resin, employed for sealing the solar cell and the synthetic rubber or soft polyvinyl chloride constituting the protective frame are difficult to adhere with, the adhesion with the adhesive material is executed after the contact faces of the resin 404 and the protective frame 403 are pretreated with plasma, strong acid, or strong alkali, for facilitating the adhesion.
Although the solar cells are sometimes use indoors under the light of fluorescent lamps, those used outdoors are required to have sufficient durability to the influence of various ambient conditions such as high temperature, low temperature, high humidity, rain, wind, etc. For this reason, the conventional solar cell module is usually composed of a seal portion 4040 for the solar cell device and a frame portion 403.
FIG. 2 is a schematic cross-sectional view of another conventional prior art solar cell module.
In a laminate member 21 constituting the solar cell module, the light-receiving face (upper face in the drawing) of a solar cell device 22 is covered, via an adhesive material 23, by a sheet-like surface protecting material 25 composed of transparent resin, while the rear face (lower face) of the device 22 is covered, via an adhesive material 23, by sheet-like rear face protecting material 25. Said coverings are provided by vacuum lamination, and the solar cell device 22 is hermetically sealed inside. The laminate member 21 is cut at positions outside the solar cell device 22, and the cut faces constitute the end faces 21c, 21d of said laminar member 21.
Aluminum frames 26, 27 for supporting the laminate member 21 are respectively provided with grooves 26a, 27a, into which are respectively inserted the edge portions 21a, 21b of the laminate member 21. Fillers 26f, 27f, for example of silicone rubber are provided in the gaps between the edges 21a, 21b and the grooves 26a, 27a, in order to prevent intrusion of water and vapor into the interior of the laminate member 21.
The solar cell modules constructed as shown in FIGS. 1 and 2 are positioned outdoors and used under various climatic conditions such as high temperature, low temperature, high humidity, wind, rain, etc.
However, the adhesive strength still is not sufficiently high even with the above-mentioned pretreatment, and the frames 403, 26, 27 may be dismantled when a strong external force is applied.
Adequate reliability cannot be attained even when the adhesive strength is increased by the above-mentioned pretreatment prior to the adhesion, the frames 403, 26, 27 may be dislodged from the solar cell module after prolonged outdoor use or by a strong external force.
Such dislodging of frames leads to peeling of the covering material of the solar cell from the end faces thereof, thus deteriorating the quality of the solar cell.
Also the filler, for example of silicone rubber, filled in the gaps between the frame grooves and the edge portions of the covering material as in the solar cell module shown in FIG. 2, often does not have a sufficiently low moisture permeability even though the water absorbability is low. Besides, the complete filling of said gaps with the filler is difficult, and said gaps eventually remain incompletely filled. As a result, moisture enters the grooves in the course of use of the solar cell and eventually reaches the solar cell device through the cut end faces of the module, thereby causing shortcircuiting of the solar cell device or destruction thereof by peeling of the thin film thereof.